The propagation of short pulses relies on managing the group velocity dispersion in the propagation medium. For most applications, the management of second order dispersion is of primary concern. Dispersion results in unwanted pulse broadening, but can also be harnessed for interesting nonlinear effects such as four-wave mixing, optical pulse compression, and supercontinuum generation. The trend towards faster optical information processing entails the use of wavelength division multiplexing (WDM) and optical time division multiplexing (OTDM). For successful OTDM, optical pulses are expected to become narrower to accommodate higher data rates and hence more susceptible to both second and higher order dispersion.
The dispersion length and the third order dispersion (TOD) length are measures of the propagation length beyond which the second and third order dispersion (TOD) respectively in the propagation medium start to become important. The dispersion length is proportional to the square of the pulse width and inversely proportional to the second order dispersion of the medium, while the TOD length is proportional to the cube of the pulse width, and inversely proportional to the TOD of the medium. It follows that optical pulses with shorter temporal widths have a shorter dispersion length and TOD length. The issue of second and third order dispersion and their pulse broadening effects in single mode fibers first arose over three decades ago. To resolve the issue of pulse broadening from dispersion, several compensators have been demonstrated for both second order and third order dispersion, mostly using optical fiber platforms.
Nanophotonics for integration of various information systems on a chip using the CMOS (complementary metal-oxide-semiconductor) compatible Silicon on Insulator (SOI) platform provides the same advantages as CMOS in microelectronics—reduced cost, increased performance, compact components with complex functionalities. Because of the high index contrast of silicon with respect to its cladding and the fact that light is highly confined in the core, the group velocity dispersion of silicon waveguides can exceed three orders of magnitude compared to single mode optical fibers. The proliferation of SOI based nanophotonics, coupled with the need to support high data rates on this platform, implies that both second and third order dispersion will become increasingly important. The TOD of silicon waveguides has been characterized to be up to three orders of magnitude larger than that in single mode optical fibers. In addition, SOI waveguides engineered to have close to zero second order dispersion would experience much more pronounced effects from TOD. This further strengthens the importance of dispersion engineering in photonic wires.